Conventionally, a vehicle headlight apparatus is arranged so that the optical axis directions of headlights provided on a front plane of a vehicle can be changed within a plane which is located substantially parallel to a plane of a road in response to a steering angle of a steering wheel (JP61-211146A).
A driver of a vehicle generally performs a driving operation while observing a road extending in a forward direction. In a case that there is a curvature change in a forward road shape, there are some possibilities that a traveling direction of the vehicle when the above steering angle is kept constant is not always made coincident with the actual road direction. As a result, in the above vehicle headlight apparatus, it is practically difficult that the optical axes of the headlights are directed to a road succeeding to a curved road which the vehicle driver wants to see under such a condition that the curvature of a road is rapidly varying, for instance, a road changing from straight to curved.
Under such a circumstance, a navigation-cooperated control type vehicle headlight apparatus is proposed (for instance, U.S. Pat. No. 5,588,733 (JP 3111153)). This navigation-cooperated control type vehicle headlight apparatus is arranged by combining with a navigation system in order to accept a curvature change in shapes of forward roads. In this navigation system, positional information detected by such a position sensing device as GPS (Global Positioning System) is related to map information. This vehicle headlight apparatus controls optical axis directions of the headlights in cooperation with the navigation system.
Since such a navigation-cooperated control type vehicle headlight apparatus may acquire the information related to structures of the forward roads in advance, even under such a travel condition that the road curvatures are varied, the optical axes of the headlights can be directed in the proper manner.
However, the conventional navigation-cooperated control type vehicle headlight apparatus is not satisfactory. Specifically, if the precision of the electronic map information provided by the navigation system is not sufficiently high, then this vehicle headlight apparatus can hardly control the optical axes of the headlights in the proper manner.
For instance, there remains an error in a position of an inflection point which can be recognized by the vehicle headlight apparatus, and there is a deviation between this recognized inflection point and the inflection point (i.e., junction point between straight road and corner road) of an actual road. Therefore, when a vehicle enters from a straight road into a curved road, there are such possibilities that timing for adjusting the optical axes of the headlights is excessively delayed, or excessively led.
Furthermore, in some cases branch roads are contained in the structure of a forward road for the vehicle. If intention of the vehicle driver cannot be grasped who determines whether this vehicle enters any one of these branch directions, the optical axes directions of the headlights cannot be properly adjusted.
Also, JP2002-225617A discloses an automatic optical axis direction adjusting apparatus for a vehicle headlight. This conventional automatic optical axis direction adjusting apparatus can properly irradiate light beams to the forward road plane of the vehicle irrespective of whether the travel destination has been inputted/set by utilizing the route guidance function in the navigation system (navigation apparatus) mounted on the vehicle.
In this conventional automatic optical axis direction adjusting apparatus for the vehicle headlight, both the optical axis directions of the right/left forward light irradiation and the irradiation ranges by the headlights can be adjusted in advance based upon the forward road information supplied from the navigation system before the steering angle of the steering wheel made by the vehicle driver is detected. Specifically, with respect to the control amounts of the headlight which are calculated based upon the forward road information supplied from the navigation system, the execution of the calculation of the control amounts of the headlights based upon the steering angle of the steering wheel by the vehicle driver is delayed. Also, since the forward road information supplied from the navigation system is not always correct, there remain some possibilities that the control amounts of the headlights are calculated based upon the incorrect forward road information in an improper manner.
As a consequence, when a swivel control operation by the steering operation of the vehicle driver is switched from the advance swivel control operation of the headlights by the navigation system, the optical axis directions of the headlights are moved. As a result, the visually recognizable characteristic of the vehicle driver for the forward road is changed, and/or the vehicle driver will have a sense of incongruity.